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An artist's depiction of the Kepler-10 system. Kepler-10c is in the foreground.
Observation data
Epoch J2000      Equinox J2000
Constellation Draco
Right ascension 19h 02m 43s
Declination +50° 14′ 29″
Apparent magnitude (V) 11.157[1]
Distance 564 ly
(173[2] pc)
Spectral type G[2]
Mass 0.910±0.021[1] M
Radius 1.065±0.009[1] R
Temperature 5708±28[1] K
Age 10.6+1.5
[1] Gyr
Other designations
KOI 72,[3] KIC 11904151,[4] GSC 03549-00354,[3] 2MASS J19024305+5014286[3]

Kepler-10, formerly known as KOI-72, is a Sun-like star in the constellation of Draco that lies 173 parsecs (564 light years) from Earth. Kepler-10 was targeted by NASA's Kepler spacecraft, as it was seen as the first star identified by the Kepler mission that could be a possible host to a small, transiting exoplanet.[5] The star is slightly less massive, slightly larger, and slightly cooler than the Sun; at an estimated 10.4 billion years in age, Kepler-10 is almost 2.6 times the age of the Sun. Kepler-10 is host to a planetary system made up of at least two planets. Kepler-10b, the first undeniably rocky planet,[5] was discovered in its orbit after eight months of observation and announced on January 10, 2011. The planet orbits its star closely, completing an orbit every 0.8 days,[6] and has a density similar to that of iron.[5] The second planet, Kepler-10c, was confirmed on May 23, 2011, based on follow-up observations by the Spitzer Space Telescope. The data shows it has an orbital period of 42.3 days and has a radius more than double that of Earth, but a higher density, making it the largest and most massive rocky planet discovered as of June 2014.[7][8][1]

Nomenclature and history[edit]

Kepler-10 was named because it was the tenth planetary system observed by the Kepler spacecraft, a NASA satellite designed to search for Earth-like planets that transit, or cross in front of, their host stars with respect to Earth. The transit slightly dims the host star; this periodic dimming effect is then noted by Kepler.[9] After eight months of observation ranging from May 2009 to January 2010, the Kepler team established Kepler-10b as the first rocky exoplanet discovered by the Kepler satellite. Kepler-10 was the first Kepler-targeted star suspected of having a small planet in orbit. Because of that, verifying Kepler's discovery was prioritized by telescopes at the W.M. Keck Observatory in Hawaii. The discovery was successfully verified.[5] Although there had been many potentially rocky exoplanets discovered in the past, Kepler-10b was the first definitively rocky planet to have been discovered.[10]

The discovery of Kepler-10b was announced to the public at a winter meeting of the American Astronomical Society on January 10, 2011 in Seattle.[10] On May 23, 2011, the existence of Kepler-10c was confirmed at the 218th AAS meeting in Boston.[11]


Kepler-10 is a G-type star, like the Sun. With a mass of 0.895 (± 0.06) Msun and a radius of 1.056 (± 0.021) Rsun, the star is approximately 10% smaller than and 5% wider than the Sun. The metallicity of Kepler-10, as measured in [Fe/H] (the amount of iron in the star), is -0.15 (± 0.04); this means that Kepler-10 is about 70% as metal-rich as the Sun. Metallicity tends to play a large role in the formation of planets, determining if they form, and what kind of planet they will form.[12] In addition, Kepler-10 is estimated to be 11.9 billion years old and to have an effective temperature of 5627 (± 44) K;[2] To compare, the Sun is younger and hotter, with an age of 4.6 billion years[13] and an effective temperature of 5778 K.[14]

Kepler-10 is located at a distance of 173 (± 27) parsecs from the Earth, which equates to approximately 564 light years. Also, Kepler-10's apparent magnitude, or brightness as seen from Earth, is 10.96; it therefore cannot be seen with the naked eye.[2]

An artist's impression of planet Kepler-10b.

Planetary system[edit]

Per the usual exoplanet nomenclature, the first planet discovered to be orbiting Kepler-10 is called Kepler-10b. Announced in 2011, it was the first rocky planet identified outside the Solar system. The planet has a mass that is 3.33±0.49 times that of Earth's and a radius that is 1.47+0.03
times that of Earth.[1] The planet orbits Kepler-10 at a distance of 0.01684 AU every 0.8375 days; this can be compared to the orbit and orbital period of planet Mercury, which circles the Sun at a distance of 0.3871 AU every 87.97 days.[15] Because the planet orbits so closely to its star, its eccentricity is virtually zero. It, thus, has an extremely circular orbit.[6]

Kepler-10c[7] was also discovered by NASA's Kepler Mission,[16] the second exoplanet found to orbit Kepler-10. Radial-velocity measurements of the body suggest that it has a mass of 17.2±1.9 Earth masses and a radius of 2.35 Earth radii, making it the largest known rocky planet as of 2014. Kepler-10c would orbit Kepler-10 at a distance of 0.24 AU every 45.29 days.[1]

The Kepler-10 planetary system[6]
(in order from star)
Mass Semimajor axis
Orbital period
Eccentricity Inclination Radius
b 3.33±0.49 M 0.01684 0.837495 0 84.8+3.2
c 17.2±1.9 M 0.2410 45.29485 0 89.59+0.25

See also[edit]


  1. ^ a b c d e f g h The Kepler-10 planetary system revisited by HARPS-N: A hot rocky world and a solid Neptune-mass planet, Xavier Dumusque, Aldo S. Bonomo, Raphaelle D. Haywood, Luca Malavolta, Damien Segransan, Lars A. Buchhave, Andrew Collier Cameron, David W. Latham, Emilio Molinari, Francesco Pepe, Stephane Udry, David Charbonneau, Rosario Cosentino, Courtney D. Dressing, Pedro Figueira, Aldo F. M. Fiorenzano, Sara Gettel, Avet Harutyunyan, Keith Horne, Mercedes Lopez-Morales, Christophe Lovis, Michel Mayor, Giusi Micela, Fatemeh Motalebi, Valerio Nascimbeni, David F. Phillips, Giampaolo Piotto, Don Pollacco, Didier Queloz, Ken Rice, Dimitar Sasselov, Alessandro Sozzetti, Andrew Szentgyorgyi, Chris Watson, (Submitted on 30 May 2014)
  2. ^ a b c d "Notes for star Kepler-10". Extrasolar Planets Encyclopaedia. 2011. Retrieved 13 March 2011. 
  3. ^ a b c "Kepler-10 -- Star". SIMBAD. Retrieved 2011-02-01. 
  4. ^ Batalha, N. M.; et al. (2011). "Kepler's First Rocky Planet: Kepler-10b". The Astrophysical Journal 729: 27. arXiv:1102.0605. Bibcode:2011ApJ...729...27B. doi:10.1088/0004-637X/729/1/27. 
  5. ^ a b c d Perrotto, Trent J.; Hoover, Rachel (10 January 2011). "NASA'S Kepler Mission Discovers Its First Rocky Planet". Ames Research Center. NASA. Retrieved 13 March 2011. 
  6. ^ a b c "Summary Table of Kepler Discoveries". NASA. 2011. Retrieved 13 March 2011. 
  7. ^ a b Fressin, F.; et al. (2011). "Kepler-10c, A 2.2-Earth Radius Transiting Planet In A Multiple System". arXiv:1105.4647 [astro-ph.EP].
  8. ^ Clavin, Whitney (June 2, 2014). "Astronomers Confounded By Massive Rocky World". NASA. Retrieved June 3, 2014. 
  9. ^ "Kepler: About the Mission". Kepler Mission. NASA. 2011. Retrieved 13 March 2011. 
  10. ^ a b Richard A. Lovett (10 January 2011). "NASA Finds Smallest Earthlike Planet Outside Solar System". National Geographic Society. Retrieved 13 March 2011. 
  11. ^ "Kepler Spacecraft Shows That Smaller Planets Abound". Scientific American. 2011. Retrieved 2011-05-26. 
  12. ^ Henry Bortman (12 October 2004). "Extrasolar Planets: A Matter of Metallicity". Space Daily. Retrieved 13 March 2011. 
  13. ^ Fraser Cain (16 September 2008). "How Old is the Sun?". Universe Today. Retrieved 13 March 2011. 
  14. ^ Ed Grayzeck. "Sun Fact Sheet". Goddard Space Flight Center. NASA. Retrieved 13 March 2011. 
  15. ^ David Williams (17 November 2010). "Mercury Fact Sheet". Goddard Space Flight Center. NASA. Retrieved 27 February 2011. 
  16. ^ "NASA'S Kepler Mission Discovers Its First Rocky Planet". NASA. 2011-01-10. Retrieved 2011-01-10. 

Coordinates: Sky map 19h 02m 43s, +50° 14′ 28.7″